Enhancing the activity and tuning the mechanism of formic acid oxidation at tetrahexahedral Pt nanocrystals by Au decoration

Abstract

Tetrahexahedral Pt nanocrystals (THH Pt NCs), bound by high index facets, belong to an emerging class of nanomaterials that promise to bridge the gap between model and practical electrocatalysts. The atomically stepped surfaces of THH Pt NCs are extremely active for the electrooxidation of small organic molecules but they also readily accommodate the dissociative chemisorption of such species, resulting in poisoning by strongly adsorbed CO. Formic acid oxidation is an ideal reaction for studying the balance between these competing catalyst characteristics, since it can proceed by either a direct or a CO mediated pathway. Herein, we describe electrochemical and in situ FTIR spectroscopic investigations of formic acid electrooxidation at both clean and Au adatom decorated THH Pt NC surfaces. The Au decoration leads to higher catalytic currents and enhanced CO 2 production in the low potential range. As the CO oxidation behaviour of the catalyst is not improved by the presence of the Au, it is likely that the role of the Au is to promote the direct pathway. Beyond their fundamental importance, these results are significant in the development of stable, poison resistant anodic electrocatalysts for direct formic acid fuel cells.

Enhanced formic acid oxidation on polycrystalline platinum modified by spontaneous deposition of gold. Fourier transform infrared spectroscopy studies

“…Consequently, gold blocks active sites for the indirect pathway and acts as an apparent promoter for the direct route. This assumption is in agreement with a recent work of formic acid oxidation on gold adatoms decorated tetrahexahedral Pt nanocrystals, in which high catalytic currents with enhanced CO 2 production was observed at low overpotentials [27]. However, the CO oxidation reaction was not improved by the presence of the Au, and therefore it is suggested that the role of the Au is to promote the direct pathway.…”

“…To understand the effect of formic acid exposition at controlled WE potential, the WE was immersed in 0.1 M HCOOH/0.5 M H 2 SO 4 or 0.1 M HCOOH/0.5 M HClO 4 solutions under potential control (0.25 V) during a specific time t c (1 < t c < 600 s) previous to the forward scan (denoted as exposition time ¼ t c ). Note that for short exposition times (t c < 10 s), the voltammogram looks like to those described in the literature [18], developing two anodic peaks: (I) a broad peak centered at 0.4e0.6 V, and (II) a narrow peak located at 0.8e1.0 V. Furthermore, the faradaic charge involved in both anodic peaks increases from t c 1e10 s. However, the anodic charge involved under the peak I decreases, while that for the peak II increases at t c higher than 10 s. Additionally, the position of peak I shifts towards more positive potentials at t c > 10 s.…”

“…The mechanism adopts an active reaction intermediate related to the current contribution at lower potentials (dehydrogenation path) [20], and a strong chemisorbed species, such as CO, which oxidizes at high overpotentials (dehydration path) [21,22]. It is remarkable that the current contribution associated with the oxidation of strongly adsorbed species becomes important at E > 0.6 V [18]. Stated briefly, the accepted mechanism for formic acid oxidation on Pt involves two well-defined pathways, i.e.…”

Rational Design and Synthesis of Low-Temperature Fuel Cell Electrocatalysts

“…In addition, durability was also significantly improved. Modified Au atoms on THH Pt NCs were also found to provide this promoting role in formic acid electrooxidation with increased activity and durability being observed [27].…”

“…Previous results have demonstrated that the catalytic activity of THH Pt NCs decorated by adatoms can be significantly enhanced (i.e. Ru for methanol electrooxidation [25], and Bi/Au towards formic acid electrooxidation) [26,27]. Even for low-index covered Pt nanoparticles such as Pt cubes with {100} facets, decoration with a Sn submonolayer significantly enhances catalytic activity for ethanol oxidation [28].…”